THE HISTORY OF DEVILS LAKE, WISCONSIN 357 



lake-level. The altitude of the well-site is about 965 feet. This 

 well penetrates 283 feet of glacial material without striking rock; 

 therefore the bottom of the pre-Glacial gap must be somewhere 

 below 682 feet, and the pre-Glacial gap at this point must have 

 been at least 788 feet deep, at least 500 feet deeper than it was at the 

 end of the second erosion cycle, and at least 283 feet deeper than it 

 is today. The maximum depth of this gap might be known if the 

 altitude of the lowest sub-drift bedrock in the Baraboo valley 

 between the ranges or in the Wisconsin valley south of the South 

 Range could be obtained, assuming that a stream flowed from the 

 Baraboo valley through the gap to the Wisconsin valley to the 

 south. The lowest bedrock surface obtainable in the Baraboo 

 valley east of Baraboo is at 570 feet. Assuming that the bedrock 

 in the Devils Lake gap is as low, the pre-Glacial gap was at least 

 900 feet deep. It cannot be ascertained whether the pre-Cambrian 

 gap was deeper than this or not so deep, for it cannot be determined 

 whether there are Paleozoic sediments below the bottom of the 

 present gap, nor whether the tops of the ranges were higher then 

 than now. If it be true that the bottom of the pre-Cambrian gap lies 

 at or near 340 feet, the pre-Cambrian gap was probably some- 

 thing like 200 feet deeper than the pre-Glacial gap. 



THE GLACIAL LAKE 



So far as ascertained, no glacier prior to the Wisconsin glacier 

 affected the Devils Lake gap. There have been some suggestions of 

 pre-Wisconsin drift in the vicinity, 1 but these evidences have 

 proved to be negative. It seems likely, however, that the Illinoian 

 glacier advanced almost to this district; but if it played any part in 

 the history of the lake or its basin, its effects are not now visible 

 within the district. 



As has been brought out by Salisbury and Atwood, 2 the Wiscon- 

 sin glacier formed Devils Lake and had a controlling influence in its 

 early history. As the ice moved into the district from the north- 

 east, it was divided by the ranges, one lobe advancing down the 



1 Samuel Weidman, Bull. No. 13, Wis. Geol. and Nat. Hist. Surv., pp. 99-102. 



2 R. D. Salisbury and W. W. Atwood, Bull. No. 5, Wis. Geol. and Nat. Hist. Surv., 

 pp. 132-33. 



